Researchers use pulsed excitation to generate localized 2D acoustic tweezers for spatially selective microfluidic patterning.

The dominant forcing mechanism for particle manipulation using SSAW is shown to be spatially dependent when travelling components are considered.

Ultrafast acoustic micromixers can effectively homogenize fluids in 4 milliseconds, at 8 ml min ⁻¹ flowrates providing a 50-fold improvement in throughput.

Acoustic fields have been widely used for manipulation of particles and cells within microfluidic systems. In this Letter, we explore a novel acoustofluidic phenomenon for particle patterning and focusing, where a periodic acoustic pressure field is produced parallel to internal channel boundaries with the imposition of either a traveling or standing surface acoustic wave (SAW). This effect results from the propagation and intersection of edge waves from the channel walls according to the Huygens-Fresnel principle and classical wave fronts from the substrate-fluid interface. We demonstrate versatile control over this effect to produce both one- and two-dimensional acoustic patterning from one-dimensional SAW fields and its utility for continuous particle focusing. Uniquely, this channel-guided acoustic focusing permits the generation of robust acoustic fields without channel resonance conditions and particle focusing positions that are difficult or impossible to produce otherwise.

Travelling surface acoustic waves (TSAW) can cause particles to follow the swirling patterns of acoustic streaming, collect in lines or migrate away from the sound source, this paper examines how particle size determines which one of these behaviours occur.